Because of a widespread concern over future energy needs and supplies, many and various proposals have been made or are being made to utilize alternative fuels and energy sources to supplement or replace some of the conventional sources of energy and power. Many suggestions have been made for the use of natural non-fuel sources of energy, such as wind, waves, solar heat, and hot water from geothermal sources, and the like. Proposals also have been made to store quantities of water and/or other fluids under pressure or at sites where they have potential energy to replace of supplement other sources of energy. Many suggestions have been made for use of water, compressed air, etc., as temporary energy storage in connection with intermittent power or energy sources such as the wind, wave, sun, etc. Some of these include the storage of water in underground caverns under hydrostatic pressure or pressure of compressed air, or the use of such stored water to generate power as it descends and to consume surplus energy when it is pumped back to the surface or to higher elevations during periods of low power consumption, etc. Among these are Fessenden U.S. Pat. No. 1,247,526, Claytor U.S. Pat. No. 2,230,526, and Haanens U.S. Pat. No. 3,806,733, relating to storing power obtained from wind energy for times when the wind is not blowing, etc. As far as applicant is aware, none of these schemes has been adopted on a significant commercial scale, probably because the costs of installation would be so high that a reasonable return on investment might not be obtainable.
Other proposals have been made for using non-fuel sources, such as the heat of the sun, the heat of geothermal waters, that of underground rock formations deep in the earth, and the like in various ways. Some of these have merit and may eventually become commercially important but they require further study, innovation and substantial investments of capital to be adopted widely. Proposals have been made also to recover heat from mild temperature bodies of water. Some such uses have been developed. The present invention is related to these. It contemplates the use of a very cold gas to extract heat energy from water that may be at only a moderately warm temperature, too low to generate steam or vapors having significant pressure or conventionally useful heat content. By using as working fluid a gas at very low temperature, compared to that of the water, a wide temperature gradient is available and by making use of gas entrainment in flowing streams to establish dynamic operating conditions, and to pressurize the gas, considerable useful energy may be obtained with relatively small capital investment.
Processes and equipment are well known for transferring some of the heat from a body of warm water to another body, using gas such as air as a heat transfer medium. By first effecting heat exchange between a gas and warm water, and then further heat the gas by compression, heat may be transferred by the working fluid to other bodies or systems, such as process water, space heating systems, or the air in an enclosed space, as in heating residental and other buildings occupied by people. The well known heat pump operates on this principle, using as transfer medium a condensible refrigerant gas or the like. In a conventional type of heat pump, for example, a volume of cool working gas is passed in heat exchange with a moderately warm fluid body, such as warm water, to pick up some of the heat of this water. The partially warmed gas is next compressed mechanically, by a power driven pump, to add further heat to it, or to condense it, after which it is taken to a second heat exchange stage where it gives up part of its heat to the body that is to be warmed. Thereafter, it is expanded, with consequent cooling, and returned to the first water source to pick up further heat, and the cycling is repeated. In such a process, it is to be noted that heat is taken from a lower temperature body and transferred at higher temperature, imparted by mechanical work, to another body. Of course, the conventional heat pump is reversible and can be used for refrigeration but when used to heat a body, it takes heat from a lower temperature body, adds to this heat by performing relatively expensive mechanical work on the working fluid, and then is expanded and recycled after it gives up its transferable heat.
The present invention makes use of a cycle that is just the reverse of this. Heat is taken up by a very cold working gas, from a warm or mild temperature body of fluid, such as water, cooling the water in the process. The energy taken up by the cold gas in this step is used for two general purposes, the first to build up potential energy in the system, as will be described, and the second, to obtain useful motive energy or shaft power. All other steps or components of the system are at lower temperature than the water, so this may be appropriately called an inverse heat pump (IHP) cycle or apparatus. It makes use, too, of the principle of entraining a large amount of the working gas into a rapidly flowing stream of liquid to aerate the latter, and to affect its specific gravity and velocity of flow properties so as to (1) achieve dynamic flow conditions which will be convertible into potential or pressure energy and (2) to compress the gas in a downflowing stream and thereby build up a reservoir of compressed gas above a body of water, both water and gas thereby being placed under enough pressure to do useful work as they are released from storage. Some of the individual steps or equipment to accomplish the several operations just mentioned are known in the prior art but the present invention combines them in a novel manner to achieve new and unexpected results. The present invention therefore makes use of some well known apparatus and process steps to extract energy from bodies of water and the like, which hitherto have not yielded energy in significant quantities.
The use of aeration, i.e., injection of air or other gas into an upwardly flowing column of water to lift it to a higher elevation has been known and used in the past. In a recent U.S. Pat. No. 3,808,445, to Bailey a system is proposed which would use a jet of air, injected from a compressed air source, to lift a column of water from a subterranean source to a site high above the ground. Then in time of need the water is allowed to flow down to generate power. Another step of the present process involves entraining air into water which is flowing downwardly, using the ancient principle of the trompe. The trompe was once used for supplying a stream of air to a forge or the like. It operated by entraining air bubbles, finely dispersed, into a downflowing stream of water, then letting them escape at the bottom into a closed space above the water. This placed both the water and the air under pressure to a degree related to the head of water, with its entrained bubbles, in the descending column. This principle has had some successful applications in mining in years past but has not been used in recent years, as far as the present applicant is aware, except for a use described in the Hancock et al patent, U.S. Pat. No. 3,754,147, in which the present applicant is a joint coinventor.
In the present invention, a stream of very cold gas is introduced in very small bubbles and as uniformly as possible across the cross section of an upflowing stream of water which is under some pressure. In a typical example, assume that a sizable stream of water is available from any suitable source, at a temperature of about 100.degree. F. Further, assume that the air or gas to be introduced has been precooled to a low temperature, e.g., below -100.degree. F. The temperature difference of over 200.degree. F. or more between gas and water, obviously makes it possible to transfer a large quantity of heat from water to the air. Small gas bubbles, introduced into the flowing water stream under pressure sufficient to distribute them well therein, rise with the stream accelerating its upward flow and rapidly expanding as they absorb heat, as they progressively come under lower hydraulic pressure to confine them. As a result, the velocity of the upflowing stream is greatly accelerated to the delivery point where the water and bubbles are introduced into a large quiescent separating zone. Due to the dynamic flow at high velocity, a substantial pressure is developed in the separating zone, according to the well known Bernoulli principle. The upflowing water was already under some pressure; it has been lifted to a substantially higher elevation plus being put under additional pressure when its dynamic energy has been converted, so that now its potential energy has been very considerably increased. The separating air, rising into storage above the upper water level in the storage or separating zone, is under the same elevated pressure as the separated water at its upper surface. This air can then be led out to and through an expander where it produces substantial motive power or shaft energy (e.g., in a turbine). It is very considerably cooled as it expands. In this highly cooled condition, it is next passed in transfer with another body of gas enroute to a second expander, as will be explained further. Exhaust gas from the second stage expander, which is also highly cooled, is then taken back to the point of injection into the rising stream of feed water, and that part of the process is repeated.
Meanwhile, a separate cycle of operation is taking place. The water from the separating zone, considerably cooled by its heat exchange with the cold gas, is under considerable pressure from gas above and is elevated substantially above its original point of entry into the system. It therefore has considerable potential (and pressure) energy. It is permitted to flow downwardly to considerable depth, preferably below the ground level, and at a relatively high velocity. As it does so, another stream of air or other gas is aspirated or injected by venturi action to aerate this downflowing stream with myriads of small bubbles. As the water continues its downward flow, these bubbles are compressed and become progressively smaller. The act of compressing them, which is done isothermally or essentially so, adds heat energy to them, according to well known gas laws. If the gas is cold when it enters, which is preferred, it first may take up a small amount of heat from the downflowing water stream, but the compression tends to counteract and to overcome this cooling process so, in most cases, the gas adds some heat overall to the water. Or to state it another way, the heat added to the gas by compression is taken up by the water. In the exemplary case mentioned above, assuming the water is at a temperature of about 100.degree. F., at the outset, it may be cooled to about 88.degree. F. by addition of very cold air in adequate quantity as it flows up into the separating zone. When it flows down, cold air aspirated into it may reduce this slightly at first, but ordinarily there will be a small temperature rise, of the order of two or three degrees F.
This downflowing water, and the gas or air bubbles which accompany it, are discharged upwardly in a storage or pressure chamber which may be hundreds of feet below the surface of the ground. Depending on the depth, and on the flow velocity and initial pressure on the downflowing stream of water, which acts as a gas compressor as it descends, pressure of the gas in the lower storage zone may be of the order of 200 psig. or more, and the applied pressure on the water will be the same. The air, or other gas may be taken from this compressed storage directly through a second expander. But preferably, it is taken in heat exchange with the exhaust gas from the first expanders to warm the latter somewhat and to cool itself before it enters the expander. The reason for this is that this gas, on exhaust from the second expander, is to be at the very cool temperature needed for injection into the original feed water, as previously explained.
The water in storage under pressure in the subterranean cavity (or other pressure site), may be released through a pressure control valve, to drive a water motor and generate additional motive power. Thereafter, if desired, it may be returned to the source at a significantly lower temperature than it had in the first place.
Variations and modifications of the system may include the use of a liquefied normally "permanent gas", such as liquid nitrogen, in place of the very cold air introduced into the rising stream of water. This has the advantage of picking up considerable additional heat from the heat source liquid, as the cold liquid is gasified. Also, various water sources may be used. A particularly suitable one for some situations is the partly cooled or condensed feed water at a large commercial steam power generating plant, which is often available at a temperature of about 100.degree. or more. The present system, using a very cold gas as the aerating and water lifting medium, is efficient in using such water. In fact, the use of water at substantially higher temperature is not as much superior as one might expect. A wide gradient or temperature difference between water and gas temperatures at the point where they are first mixed together is more important than the availability of hotter water. In lieu of water from a steam plant, warm water from ponds, lakes, rivers, and especially from irrigation reservoirs and canals in the warmer parts of the world, is very suitable for use in the present invention. Warm well water or that from other ground formations may of course be used as the main heat source. In a modification mentioned above, very cold liquefied gas such as nitrogen may be introduced in finely divided form into an upflowing stream of the feed water, to effect efficient heat exchange and to rapidly establish dynamic flow conditions. The condensed liquid particles, introduced in finely divided form, rapidly vaporize and they expand very rapidly as they absorb heat from the water, thereby rapidly accelerating the upward flow so that the rising stream, when it enters a quiescent zone at high velocity converts its dynamic flow energy to potential energy, putting it under higher pressure.
A further aspect of the invention is a specific application for raising warm surface or underground water to a higher level, making use of available heat in the water to supply the required lifting energy.
This second modification may involve more or less the same steps as described in connection with the first, where air is used as the working fluid but preferably the second system is used not only to generate motive power or shaft energy but to reliquify the nitrogen and/or to liquify atmospheric air. From such liquid air, various valuable commercial products may be obtained, in addition to the energy, such as liquid or high pressure gaseous oxygen, argon, carbon dioxide, etc., as will be readily understood by those skilled in the art.
To redefine the invention briefly, in a first embodiment, a system and process are described in which a large volume liquid, such as warm water, is raised from a low point by introducing into the liquid a stream of finely dispersed very cold air or other gas to aerate the rising column of liquid. This extracts heat from it, and accelerates its upward flow to a high velocity, thereby imparting considerably dynamic energy to the rising liquid stream. The aerated stream is introduced into a quiescent zone, a closed vessel of substantial capacity, where the entrained gas separates, but both the liquid and the gas are placed under substantial pressure. The pressurized gas is taken to an expander where it does useful work and is very substantially cooled in expanding. This cooled gas is heat exchanged with another stream of gas enroute to a second expander; thereby it is warmed somewhat. It may be discharged to the atmosphere but preferably it is used in the next step to be described.
The water or other liquid in the separating chamber, under substantial pressure and at a relatively high elevation, has substantial potential and pressure energy. It is allowed to flow downwardly at velocity sufficient to aspirate or draw in air or gas supplied through a venturi device. This gas, in the form of fine bubbles, is carried down to the full depth of a subterranean chamber and the bubbles are compressed to put them under the full pressure head of the descending water stream. The gas entrained may equal or exceed by volume the volume of the water. Ratios of four volumes of gas to one of water have been achieved, under standard gas conditions. When the gas is released from the water in the storage compartment, it accumulates under pressure sufficient to hold the water to a level slightly above the outlet. This pressure is maintained by a pressure regulating valve in the water outlet line. The gas is released to flow to a second expander, first passing in heat exchange with the exhaust gas from the first expander, to reduce its own temperature. It is cooled further to very low temperature in passing through the second expander and then is returned to the disperser for aerating and assisting in lifting the water in the first riser column.
The water in the subterranean compartment, which is held under high pressure, may be released through the pressure control valve which stabilizes its level in the storage compartment. Then it is passed through a water motor before being returned to the warm water source or used for other purposes. Thus, there are three sources of motive power or shaft energy, viz., the two gas expanders and the water motor. The first of these normally produces by far the largest amount of energy.
In the second modification system, a cryogenic liquid, such as liquid nitrogen is led through an insulated pipe to the bottom of a deep column of water and is then sprayed upwardly into a rising column to assist that water to rise. Preferably, the nitrogen is still primarily in liquid condition as it enters the water. It is almost instantly vaporized to produce gas bubbles, and the bubbles expand rapidly as heat is extracted from the water and as they ascend under reducing pressure conditions. As a result, the stream flows up at high velocity, achieving high dynamic energy which is converted, to a large extent, to potential energy in the next column where the gas separates from the water and gas and water are stored momentarily. Additional dynamic energy is imparted to the system in a second column within a larger shaft where the water next flows down to great depth, drawing in the same gas again through a venturi or aspirator. This gas is placed under further compression by the descending stream, in this example. Gas and water emerge from the upturned end of this descender column, near the bottom of this larger shaft. The gas separates from water as before and accumulates under pressure above the water level, which is only a short distance above the outlet. This compressed gas may, in part, be drawn off now to flow through a first expander and produce useful power; at least part of it preferaby is passed into another downflowing compressor column wherein atmospheric air is drawn in through a venturi or aspirator from the atmosphere. This air is compressed as before; the water and air separate at the bottom of this shaft as before, and the air is drawn off at the top under control of a pressure regulator, to operate a second expander and be cooled to low temperature. The separated water is passed through a water motor to generate additional motive energy. In addition, if desired, part of the water from the first compressor may be added to that from the second to augment the flow to the water motor. This depends on the relative capacities and flows of the two downflowing water compressor columns.
Additional modifications or variations will be described herein below, being logical extensions and variations of those already briefly described. Further modifications may suggest themselves to those skilled in the art, as this description continues in greater detail. For this purpose, reference will now be made to the accompanying drawings.